[css-navigation-1] Restrict at in both @navigation and :link-to() to navigations.

This restricts matching of at: in both @navigation and :link-to() to
when a navigation is currently active.

This defines the term "current at URL" to help with that, and also
renames the existing "current other URL" term to "current with URL" to
keep internal and author-exposed terminology consistent.

Author: dbaron

css-navigation-1/Overview.bs

@@ -268,15 +268,16 @@ as follows:
 
 : <<navigation-location-test>>
 ::    : at: <<navigation-location>>
-    :: The result is whether the result of
+    :: The result is true if
+        the [=current at URL=] <var>at</var> of the document is non-null and
         [=URL pattern/match|match a URL pattern=] is non-null
         given <var>urlPattern</var> as
         the [=navigation location URL pattern=] of <<navigation-location>>
-        and <var>input</var> as the document's [=Document/URL=].
+        and <var>input</var> as <var>at</var>.
 
     : with: <<navigation-location>>
     :: The result is true if
-        the [=current other URL=] <var>other</var> of the document is non-null and
+        the [=current with URL=] <var>other</var> of the document is non-null and
         [=URL pattern/match|match a URL pattern=] is non-null when
         given <var>urlPattern</var> as
         the [=navigation location URL pattern=] of <<navigation-location>>
@@ -523,9 +524,9 @@ if the following steps return true:
     of the <<navigation-match>>.
 1. Let <var>navigationURL</var> be:
     : If <var>matchRelation</var> is ''at'',
-    :: the document's [[=Document/URL=]].
+    :: the <a>current at URL</a> of the document.
     : Otherwise, if <var>matchRelation</var> is ''with'',
-    :: the <a>current other URL</a> of the document.
+    :: the <a>current with URL</a> of the document.
     : Otherwise, if <var>matchRelation</var> is ''from'',
     :: the <a>current from URL</a> of the document.
     : Otherwise (Assert: <var>matchRelation</var> is ''to''),
@@ -556,8 +557,8 @@ NOTE: Some of the design discussion for this feature has been in
 <h2 id="current-nav-urls">Definitions of current navigation state</h2>
 
 Both the ''@navigation'' rule and the '':link-to()'' pseudo-class
-rely on the following definitions of
-the [=current other URL=], [=current from URL=], and [=current to URL=].
+rely on the following definitions of [=current at URL=]
+the [=current with URL=], [=current from URL=], and [=current to URL=].
 
 The <dfn>current from URL</dfn> of a [=/document=] is a URL or null.
 It is defined as follows:
@@ -648,10 +649,17 @@ ISSUE: The above definitions of from and to apparently don't work right
 if you start a same-document navigation (e.g., with {{History/pushState}})
 in the middle of a cross-document navigation.
 
-The <dfn>current other URL</dfn> of a [=/document=] is a URL or null.
+The <dfn>current at URL</dfn> of a [=/document=] is a URL or null.
+It is defined as follows:
+
+1. ISSUE: Write this!  (It should be null if there is no active navigation,
+    and the same as the document's [=Document/URL=] if there is.)
+
+The <dfn>current with URL</dfn> of a [=/document=] is a URL or null.
 It is defined as follows:
 
-1. ISSUE: Write this!
+1. ISSUE: Write this!  (It should be like [=current to URL=] and [=current from URL=]
+    but always referring to the other Document in the navigation.)
 
 The <dfn>current navigation type</dfn> of a [=/document=] is a {{NavigationType}} or null.
 It is defined as follows: